A project is proposed to continue the study of (1) primary structure of human gastric proteases, pepsin and gastricsin, (2) the intramolecular activation mechanism of pepsinogen -- as a model of the zymogen activation in acid proteases, and (3) the mechanism of pepsin like enzymes. BIBLIOGRAPHIC REFERENCES: Tang, J., "Pepsin and Pepsinogen: Models for Carboxyl (Acid) Proteases and Their Zymogens", Trends in Biochemical Sciences, 1, 205-208 (1976). Tang, J., "Acid Proteases Come of Age", Nature, 266, 119-120 (1977).